1. Technical Field
The present disclosure relates to an optical scanning projection system, and more particularly, to an optical scanning projection system for improving safety in use and compensating image distortions.
2. Related Art
Currently, the micro-projection system technique may be classified into two categories. The first category is laser scanning projection technique using laser light as a light source, and the second category is Digital Light Process (DLP) technique or Liquid Crystal on Silicon (LCoS) technique using a Light Emitting Diode (LED) as a light source. As the light source is a LED, there are some problems with the micro-projection system. First, the operating temperature of the micro-projection system may adversely affect the service life and the luminescence efficiency of the LED. Second, the unsatisfactory photoelectric conversion efficiency of the LED leads to that raising the brightness of the micro-projection system is difficult. Moreover, when being turned on for a considerable period, the LED usually causes high power consumption of the system. Accordingly, when LED is used as a light source of the light engine with delicate focus lens set, the structure of the light engine becomes complicated.
With respect to the micro-projection system employing a laser as the light source, because the laser has a wider color gamut and better color saturation, the projected frame is brighter and more colorful. Besides, the laser scanning projection technique merely uses a single micro-mirror to perform the scanning projection to form the projection frame. However, the DLP technique needs many micro-mirrors, which causes difficulties in the yield and cost control. Therefore, comparing with the DLP technique, the laser scanning projection technique has the advantages of better yield and low cost. Furthermore, as the laser light has high brightness, good directivity, and may be projected on any plane, the complicated focus lens set is not required when the laser is used as the light source. Accordingly, the structure of the light engine using LED as the light source is simple, and, therefore, the micro-projection system employing the laser scanning projection technique is small in size and is easy to be built into an electronic device.
Since the laser is a high-power light source, the micro-projection system employing the laser scanning projection technique (hereinafter, referred to as the laser scanning projection system) needs to strictly conform to the laser safety specification. Generally, the laser scanning projection system meets the specification in normal operation. However, when the scanning element (i.e. the micro-mirror) is faulty and, therefore, cannot transform the laser light into the projection frame, a high brightness single light spot which is hazardous to the viewer's eyes will be formed. Moreover, during the laser scanning projection system carrying out the dynamic projection, the content of the projection frames changes quickly. Such quick changes then change the power of the laser light, so that the temperature of the scanning element changes quickly. However, such quick temperature changes influence the amplitude of the scanning element and, therefore, cause the misalignment of the scanning frames played sequentially. As a result, the image distortion and the frame blur are generated. Therefore, it is the trend in research and development for the practitioners in the field on how to solve the safety problem and the frame blur generated in dynamic projection of the laser scanning projection system.